1. Field of the Invention
This invention relates to a supercharged diesel engine.
2. Description of the Related Art
In general, a diesel engine is equipped with a turbocharger for improving the output power or torque of the diesel engine. In the turbocharger, since a compressor is of the centrifugal type, a pressure to be supplied to the engine will not increase while an output pressure of a turbine remains low. Thus, while the engine is in a low speed region, the power efficiency of the turbocharger is not good because it is difficult to increase output power or torque of the engine. Moreover the turbocharger has a characteristic turbo-lag so that it takes a long time for power to build up after depressing the accelerator if the car is equipped with a turbocharged diesel engine.
On the other hand, a supercharger is often equipped to a gasoline engine in order to increase its output power or torque instead of the turbocharger. The supercharger does not have the above problems.
In light of this, when the diesel engine is equipped with the supercharger, it is necessary to make the rotational speed amplification between an output shaft of the diesel engine and the supercharger larger than that between an output shaft of the gasoline engine and the supercharger.
In general, the output shaft of the diesel engine is connected to the supercharger via belt means and clutch means. The clutch means is held at its disengaged condition and engaged condition while the supercharger is in its rest condition and operation condition, respectively.
As the clutch means changes from the engaged condition to the disengaed condition, the differential rotational number across the clutch or the rotational number of the diesel engine relative to that of the supercharger becomes large. Therefore the load to the clutch means upon its engagement becomes so big that opposed friction surfaces of the clutch wear rapidly and a danger may occur that the supercharging of the engine becomes impossible.